This invention relates to large rotary electrical machines, e.g. with ratings of 1 MW and upwards, having a generally horizontal axis of rotation.
Large rotary electrical machines, for example generators of turbine-generator sets, have a stator construction comprising a generally annular outer casing which carries the stator core and the stator winding either directly or through an inner annular core frame (see "The Mechanical Design of Large Turbogenerators", B. A. Marlow, Proc. Instn. Mech. Engrs., Vol. 200 (1986) No. 135). In each case outer casing or the core frame has struts extending radially inwards that provide support and location for the core laminations. Heavy end plates, sometimes secured together by through bolts, hold the laminations together under a relatively high compressive force in order to limit axial thermal expansion and vibration.
To assemble such cores, the outer casing or the core frame, as the case may be, is first constructed and is fitted with one end plate. It is then stood with its axis vertical and the end plate lowermost so that the laminations, usually in segmental form, can be dropped individually into the frame and fitted into place. The other end plate can then be added and the core laminations clamped, after which the core frame is returned to a horizontal position for the remaining assembly operations, including fitting the windings. The construction of the core frame and fitting the core laminations into it, which typically can take 16-20 weeks for a 500 MW generator, adds significantly to the costs of manufacture as well as requiring significant capital investment for plant capable of handling the core frame during the various operations.